The cultist will say:"Your lies fall on deaf ears, Deceiver. The True Dragonborn comes... You are but his shadow". They attack you.

This starts the Dragonborn questline. You have to find out who sent the Cultists after you.

Kill the cultists, and loot their bodies for Cultists' Orders:

Read Cultists' Orders. Their orders were to kill you. They were instructed to board the Northern Maiden docked at Raven Rock and to take it to Windhelm. So their boat must still be at Windhelm, and this will be your next destination.

Hello, to start Dragonborn is there a minimum quest requirement:
You need to complete the 5th main quest "The Way of the Voice".
If you not talk with Greybeards, will not appear the people with
masks (Cultists of Miraak).